Industrial hygienists estimate inhaled concentrations of airborne contaminants using "personal" samples, which are almost always taken at the lapel of the sampled subject (i.e., a worker). Despite the importance of the assumption that lapel samples are representative of inhaled concentrations, it has not been convincingly demonstrated by published research, and significant doubts remain that concentrations at the lapel are always representative of inhaled exposures. It is quite plausible that lapel samples are unrepresentative of inhaled concentrations for some exposure conditions and that lapel samples bias results differently for different work environments. Given the complexity of the fluid flows near the body and the high variability of conditions in the workplace, modeling the relationship between lapel and inhaled concentrations for all exposure conditions is practicable only with CFD. However, with CFD and verification with experimental data, it should be possible to find the effects of important variables on: 1) the levels of inhaled concentrations, and 2) the errors associated with use of a surrogate sampling site instead of inhaled concentrations. It is reasonable to suspect that one or more adequate surrogate sites for inhaled concentrations can be found among the following locations: lapel, neck, sternoclavicular region, cheek, or forehead. The proposed study will compare tracer gas and vapor concentrations taken at these sites during highly challenging conditions. Humans and mannequins in a wind tunnel will be sampled under various conditions of cross-draft velocity, cross- draft orientation, and source location to find the conditions that produce the greatest deviations between inhaled samples and its surrogates. The experiments will also explore the effects of breathing on sampling error at the sampling sites. In addition, the scope of the findings will be extended by use of computational fluid dynamic (CFD) modeling This issue is important to IH practice, particularly in enforcement of OSHA standards for allowed airborne contaminant exposures, but also in epidemiological research, allocation of funds for engineering controls, and in relating exposures to biological sample concentrations. Finally, the study will allow evaluation of the efficacy of modeling human exposures using mannequins and CFD.